HARTFORD — — Robert Gentile, the mobster locked in a standoff with federal authorities over hundreds of millions of dollars in artwork stolen from Boston's Isabella Stewart Gardner Museum, pleaded guilty Wednesday to drug and gun charges.

Federal investigators have been pressing the ailing, 76-year old gangster for at least two years in the belief that he has knowledge of what became of 13 priceless paintings stolen in 1990 in the most expensive, notorious — and still unsolved — stolen art case ever.

Gentile, who was rolled into federal court Wednesday in a wheelchair, and members of his family have denied knowledge of the art or of the Gardner job during repeated interviews with law enforcement authorities and repeated appearances before a federal grand jury.

After months of unproductive talks, the FBI and federal prosecutors targeted Gentile in a drug sting and charged him a year ago with conspiring with longtime associate Andrew Parente of Hartford to sell prescription painkillers. At the time, Gentile was a fixture at a used car lot and garage on Franklin Avenue, where he cooked lunch for the handful of senior citizen mobsters still regulars in the neighborhood.

Earlier this year, Gentile was charged with being a convicted felon in possession of guns, ammunition and four silencers after successive FBI searches of his suburban ranch home in Manchester in February and March turned up what a federal magistrate called a "veritable arsenal."

In exchange for guilty pleas to six drug charges and three weapons charges, Gentile faces 46 to 57 months in prison under the terms of a plea-bargain agreement reached by his lawyer, A. Ryan McGuigan, and Assistant U.S. Attorney John Durham. The maximum sentence on each of the nine charges would have resulted in 150 years in prison.

McGuigan has suggested on prior occasions that the prosecution of his client is a bald attempt by the government to pressure "a sick old man" to produce information about an art theft that he knows nothing about.

At times during the drawn-out hearing Wednesday, Gentile seemed poised to criticize the government's evidence against him, but backed down after considering the far longer sentence he faced if U.S. District Judge Robert N. Chatigny refused to accept guilty pleas and he was convicted after a trial.

At one point, Gentile said he obtained some of the pain pills he sold under his own prescription issued for back pain. He said he agreed to sell the pills only after a government informant offered him a price that he couldn't refuse. Durham suggested that Gentile was filling the prescriptions for resale and had been obtaining pain medication from two different physicians who were not aware that they both were prescribing to him.

"I'm sorry for costing the state a lot of time and money," Gentile repeatedly told Chatigny. "I don't have many more years to fight this case, because I am a very sick man."

Asked by Chatigny whether he considered a guilty plea to be in his best interest, Gentile replied: "Yes, I do, for myself and the government, to save time. I don't have much time left."

Informed by the judge that he would have to forfeit the guns, Gentile said, "I don't want them."

As well as $22,000 in confiscated cash, the judge said.

"You can have that, too," Gentile said. "Thank you."

When Gentile appeared set to equivocate about his possession of homemade silencers, devices designed to suppress gunshots, Durham said the FBI had found a Boston gangster who could testify that he bought a silencer from Gentile in 2000.

The Gardner robbery unfolded when two men disguised as police officers talked their way into the museum about 1:30 a.m. on March 18, 1990, and shocked the art world. They bound the museum's two security guards, battered priceless paintings from their wall mounts and frames, stuffed the canvases into a little red car and disappeared.

Among the estimated $500 million in stolen masterpieces are three Rembrandts — including his only known seascape, "Storm on the Sea of Galilee" — a Vermeer, a Manet and five drawings by Degas. One source close to the investigation said Gentile is the best lead that authorities have had in 22 years.

It's "all lies," Gentile said during an earlier appearance in court.

Over half a century, Gentile has had a reputation in Hartford mostly as a hustler and a thief, according to a variety of law enforcement and underworld sources. But in the past decade or so, federal authorities have developed information suggesting that his interests were wider than originally thought, the same sources said.

Associates of Gentile have said that, in the 1990s, he began traveling regularly to Boston. He became a made, or sworn, member of a crew of the Genovese crime family operating in Boston in 1998 at age 62, according to law enforcement and other sources.

While in Boston, he also became associated with the crew of gangsters in Dorchester that included the FBI's best suspects in the Gardner job, according to the same sources.